1. Field of the Invention
The present invention relates to a light-emitting device to be used for illumination, display, communication, etc., as well as to an illumination apparatus, a display apparatus, and other systems using such a light-emitting device. The present invention also relates to an optoelectronic integrated circuit device formed by integrating a silicon IC and optical elements.
2. Description of the Background Art
Various light-emitting devices are known. However, their luminous efficiency is low, which is a major problem to be solved. Recently, low-power-consumption light sources have been required in connection with environmentally related problems and various technical developments have been made to increase their luminous efficiency. For example, in incandescent lamps, heat-radiation light is mostly infrared light and includes very little visible light, which is the main reason of low efficiency. To increase the efficiency, a measure as shown in FIG. 18 has been taken in which the glass ball of a lamp is coated with an infrared reflection film referred to as a heat mirror (see Jack Brett et al., xe2x80x9cRadiation-conserving Incandescent Lampsxe2x80x9d, J. of IES, p. 197, 1980). In FIG. 18, reference numeral 1801 denotes a glass ball having a heat mirror and numeral 1802 denotes a tungsten filament.
To increase the feedback ratio, that is, the ratio at which reflected infrared light is absorbed by the filament, fine adjustment of the filament position and other adjustments are necessary. However, the increase in feedback ratio attained by such adjustments is restricted, and hence sufficient improvement cannot be obtained.
A more straightforward measure in which the radiation itself of infrared light from a filament is suppressed has been proposed in U.S. Pat. No. 5,079,473. In this method, as shown in FIGS. 19A and 19B, an array of cavity waveguides is provided on the surface of a light-emitting body. In FIGS. 19A and 19B, reference numeral 1901 denotes a tungsten filament and numeral 1902 denotes cavities in this method, and the radiation of light in a frequency range that is lower than the cutoff frequency is suppressed by setting the cutoff frequency of the cavity waveguides at a predetermined value.
However, even in this case, infrared light is freely radiated from the regions between adjacent of the cavity waveguides. Decreasing the distance between adjacent cavity waveguides is considered to decrease the area of those regions to thereby reduce infrared radiation. However, this measure has a problem that the cutoff frequency disappears due to coupling of adjacent optical modes, that is, infrared light comes to be radiated freely contrary to the intention.
On the other hand, a display utilizing heat radiation has been reported (see Frederick Hochberg et al., xe2x80x9cA Thin-film Integrated Incandescent Display,xe2x80x9d IEEE Trans. on Electron. Devices, Vol. ED-20, No. 11, p. 1,002, 1973). That paper reports a display that utilizes heat radiation from tungsten. However, the luminous efficiency of the light-emitting portion is very low because, as described above, heat radiation light includes very little visible light. So the display as a whole has a serious problem in efficiency.
In the field of optical communication, in which lasers and LEDs are used as light sources, simpler, lower-cost light sources have been desired. In the field of silicon ICs and LSIs, the realization of optoelectronic integrated circuits have been desired. However, their application range is limited because no silicon device capable of emitting light efficiently is available, and hence an LSI and a light-emitting element need to be manufactured separately. Further, an increase in the integration density of LSIs and multi-layering of complex electric wiring are major factors that prevent a future increase in the integration density of optoelectronic integrated circuits.
As described above, although various attempts have been made to increase the efficiency of light-emitting devices, they have not succeeded in increasing the characteristic to a large extent. Further, complex electrical wiring of LSIs has prevented an increase in the integration density of optoelectronic integrated circuits.
The present invention has been made in view of the above circumstances in the art, and an object of the present invention is therefore to provide a novel light-emitting device having high luminous efficiency as well as various systems using the novel light-emitting device.
Another object of the present invention is to provide a novel optoelectronic integrated circuit device having optical wiring that replaces complex electric wiring of an LSI.
To attain the above and other objects, the present invention provides the following devices and apparatuses.
One feature of the present invention is that a light-emitting device for radiating visible light includes a light-emitting element configured to radiate first light having an intensity peak within the infrared wavelength region. A photonic crystal structure faces the light-emitting element, and the photonic crystal structure receives the first light from the light-emitting element and transmits the first light to convert the first light into second light having an intensity peak within the visible light wavelength region, and the second light is radiated from the photonic crystal structure as visible light.
A further feature of the present invention is that a light-emitting device for radiating visible light includes a first filament configured to radiate first light having an intensity peak at a first wavelength thereof. A photonic crystal structure is provided surrounding the first filament, and the photonic crystal structure receives the first light from the first filament and transmits the first light to convert the first light into the light having an intensity peak at a second wavelength thereof which is smaller than the first wavelength of the first light, and the second light is radiated from the photonic crystal structure as visible light.
Preferred embodiments of the above present inventions may include the following features (1)-(15).
(1) The photonic crystal structure includes a dielectric layer and metal bodies arranged in the dielectric layer periodically.
(2) Each of the metal bodies is a spherical body.
(3) The dielectric layer is formed of at least one material selected from the group consisting of TiO2, SiO2, Al2O3, Si, and ZrO2, and the metal bodies are formed of at least one material selected from the group consisting of Ag, Au, Cu, Fe, Co, Ni, W, In, Zn, Cr, Ti, and Pt.
(4) The light-emitting device further includes a defect portion among the metal bodies in the dielectric layer selectively, and the defect portion lacks part of the metal bodies.
(5) The defect portion includes cavities.
(6) The light-emitting device further includes dielectric bodies among the metal bodies in the dielectric layer selectively, and the dielectric bodies are different from the dielectric layer in refractive index.
(7) The photonic crystal structure includes dielectric layers and metal layers stacked alternately with the dielectric layers.
(8) Each of the dielectric layers and each of the metal layers are provided with a one-dimensional periodic structure.
(9) Each of the dielectric layers and each of the metal layers are provided with a two-dimensional periodic structure.
(10) The dielectric layers are formed of at least one material selected from the group consisting of TiO2, SiO2, Al2O3, Si, and Zro2, and the metal layers are formed of at least one material selected from the group consisting of Ag, Au, Cu, Fe, Co, Ni, W, In, Zn, Cr, Ti, and Pt.
(11) The light-emitting element is formed of at least one material selected from a group consisting of W, Si, SiC, GaN, AlN, graphite, diamond, and amorphous carbon.
(12) The first filament is provided with first holes, and the first holes are arranged periodically along a direction in which the first filament extends and corresponding to the photonic crystal structure.
(13) The first filament crosses a second filament provided with second holes, and the second holes are arranged periodically along a direction in which the second filament extends and corresponding to the photonic crystal structure.
(14) The photonic crystal structure includes a first photonic crystal body having a trench and a second photonic crystal body, and the first and second photonic crystal bodies are combined with each other with the trench interposed therebetween such that the first filament passes through the trench.
(15) The first filament is formed of at least one material selected from the group consisting of W, Si, SiC, GaN, AlN, graphite, diamond, and amorphous carbon.
A further feature of the present invention is that a display apparatus having a light-emitting device for radiating visible light includes a light-emitting element configured to radiate first light having an intensity peak within the infrared wavelength region. A photonic crystal structure is provided facing the light-emitting element, which receives the first light from the light-emitting element and transmits the first light to convert the first light into second light having an intensity peak within the visible light wavelength region, which is radiated from the photonic crystal structure as visible light. A display panel is configured to display information using the second light, and the display panel is irradiated with the second light from the backside thereof.
A further feature of the present invention is that a display apparatus having a light-emitting device for radiating visible light includes a filament configured to radiate first light having an intensity peak at a first wavelength thereof. A photonic crystal structure is provided surrounding the filament, which receives the first light from the filament and transmits the first light to convert the first light into second light having an intensity peak at a second wavelength thereof which is smaller than the first wavelength of the first light, which is radiated from the photonic crystal structure as visible light. A display panel is configured to display information using the second light, and the display panel is irradiated with the second light from the backside thereof.
Preferred embodiments of the above present inventions may include the following features (1)-(3).
(1) The display panel is a liquid crystal display panel.
(2) The display panel includes a plurality of panel portions and the light-emitting element includes a plurality of light-emitting parts, and each of the plurality of light-emitting parts is provided corresponding to each of the plurality of panel portions, and each of the panel portions is colored with a predetermined color so as to display a signal or an image by irradiating the display panel with the second light.
(3) The display panel includes a plurality of panel portions and the first filament includes a plurality of filament parts, and each of the plurality of filament parts is provided corresponding to each of the plurality of panel portions, and each of the panel portions is colored with a predetermined color so as to display a signal or an image by irradiating the display panel with the second light.
Another aspect of the present invention lies in a light-emitting device which radiates light in a desired wavelength range by light emission through heat radiation, light emission with a MIS structure, EL light emission, or fluorescent light emission, wherein a photonic crystal structure is provided so as to occupy at least a portion of a space that is close to a light-emitting portion for radiating light, whereby radiation of light in at least part of the wavelength range other than the desired wavelength range is suppressed or radiation light in at least part of the desired wavelength range is enhanced.
Further, another aspect of the present invention lies in a light-emitting device which radiates light in a desired wavelength range by light emission through heat radiation, light emission with a MIS structure, EL light emission, or fluorescent light emission, wherein a photonic crystal structure is provided so as to occupy at least a portion of a space that is close to a light-emitting portion for radiating light, whereby a polarization state or a radiation pattern of light in the desired wavelength range is controlled.
Further, the present invention provides an illumination apparatus or a display apparatus including the above-described light-emitting devices that are arranged in an array form.
The present invention provides an illumination apparatus or a display apparatus including light-emitting devices that are arranged in an array form, wherein a laser or a light-emitting diode is used as each of the light-emitting devices rather than light radiation by light emission through heat radiation, light emission with a MIS structure, EL light emission, or fluorescent light emission.
Further, the present invention provides an optoelectronic integrated circuit device including a silicon IC and the above-described light-emitting devices that are integrated with the silicon IC. An output signal of the silicon IC is input to a light emitting element (or a filament) of the light-emitting device to cause the light emitting element (or the filament) to radiate light.
Still further, the present invention provides an optoelectronic integrated circuit device including a silicon IC circuit device and a light-emitting body utilizing heat radiation, and at least one of an optical modulator having a photonic crystal structure, an optical waveguide having a photonic crystal structure, an optical filter having a photonic crystal structure, and a photodetector having a photonic crystal structure, at least one of the optical modulator, the optical waveguide, the optical filter, and the photodetector being integrated with the silicon IC circuit device.
In the present invention, the photonic crystal structure is provided so as to occupy at least a portion of a space that is close to the light-emitting portion for radiating light, whereby radiation of light in at least part of the wavelength range other than a desired wavelength range is suppressed or radiation light in at least part of the desired wavelength range is enhanced. For example, a visible wavelength range can be set as the desired wavelength range and radiation of infrared light can be suppressed.
The light emission spectrum of the conventional heat radiation is represented by the black body radiation spectrum that is determined by Planck""s equation multiplied by emissivity that is specific to a radiation material. When the temperature of the light-emitting portion is about 2,000xc2x0 C., visible light accounts for only a small part of the spectrum. The term xe2x80x9cphotonic crystal structurexe2x80x9d as used herein means an artificial crystal that is given optical anisotropy or dispersion by forming an optical band by arranging two or more kinds of media periodically or at different pitches or that is prohibited from propagating light in a particular wavelength range by generating a band gap. The crystal structure may be of one-dimensional, two-dimensional, or three-dimensional.
The concept of the photonic band gap has been proposed in a paper by E. Yablonovitch, Phys. Rev. Lett., 58, p. 2,059, 1987. When disposed close to the above-mentioned light-emitting portion, the photonic crystal can prevent the light-emitting portion from radiating light in a particular wavelength range. For example, if the optical band gap is set in an infrared range, radiation of infrared light can be suppressed and the proportion of visible light can be increased.
According to another aspect of the present invention, the photonic crystal structure is provided so as to occupy at least a portion of a space that is close to the light-emitting portion for radiating light, whereby a polarization state or a radiation pattern of light in a desired wavelength range is controlled. In this case, actually usable light of radiation light in the desirable wavelength range is enhanced, whereby the effective luminous efficiency can be increased.
The above description relates to the case in which the present invention is directed to enhancement of visible light. Similarly, it is possible to make a setting so that near infrared light that is used for the optical communication, particularly light in the vicinity of 1,300 nm or 1,550 nm can be emitted efficiently.
Another feature of the present invention is that the photonic band structure includes at least a metal. In that case, the optical band gap can be particularly widened, whereby the light emission spectrum can be controlled over a wide wavelength range from visible light to far infrared light. That makes it possible to realize more efficient light sources.
Further, the present invention makes it possible to realize an illumination apparatus and a display apparatus that are not only highly efficient, but also high in illuminance by arranging such highly efficient light-emitting devices in an array form. In particular, when a polarization-controlled light source is used as the backlight of a liquid crystal display apparatus, the efficiency can greatly be increased because of the absence of a polarization component that is wasted conventionally.
The present invention makes it possible to easily integrate a silicon LSI with optical elements by forming the light-emitting body portion that causes heat radiation using silicon or tungsten, for example. Further, by combining a light-emitting element that is formed on an LSI and which utilizes heat radiation with, for example, an optical waveguide that utilizes a photonic crystal structure, the present invention makes it possible to replace at least part of conventional electric wiring with optical wiring to simplify wiring, and thereby makes it possible to easily increase the integration density of an optoelectronic LSI.